Hydraulic Containment at Landfill Sites

Kane Mitchell, Environmental Scientist, Environ Australia Pty Ltd, Hunter Valley

A hydraulic containment system of some description is commonly required to abate the offsite migration of leachate and/or contaminated groundwater at landfill sites, and to a lesser extent other contaminated sites (i.e. industrial facilities). In Australia, these systems typically comprise pumping leachate/groundwater from a series of extraction bores to maintain an inward hydraulic gradient, with the extracted leachate/groundwater transferred to a treatment plant, or to sewer. The construction of a cut-off wall may be a more appropriate approach where saltwater intrusion is an issue, subsurface conditions are not favourable for groundwater extraction (i.e. low hydraulic conductivity aquifer) or a high level of certainty is required regarding the containment of the targeted groundwater/leachate due to site sensitivity. The lecture will provide a brief background on the application and limitations of cut-off walls in groundwater remediation projects (landfill and other contaminated sites) as well as a case study of a groundwater remediation project conducted at a 40Ha former landfill site situated adjacent to a canal in the Sydney metropolitan area, including discussion of: the design and construction of a soil/bentonite cut-off wall (1.5km in length, 0.8m wide, max. depth 15m) and associated leachate collection/treatment system; the usefulness of a full scale pilot test conducted prior to full commitment to the soil/bentonite slurry approach; the development of an innovative means of validating the performance of cut-off walls in tidal groundwater systems; The demonstrated performance of the wall to date.

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